The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty.
The present invention relates generally to gas turbine engines and, more specifically, to a gas turbine engine having a compliant casing.
The efficiency of gas turbine engines depends in part on the dimensional clearances between the inner components. Generally, it is important that the gap between the rotor tip and casing be made as small as practical. As the gap clearance increases, tip clearance vortices increase, resulting in the reduction of mass flow, pressure ratio, efficiency and stall margin.
While the design tip clearance described above is desirably kept to a minimum, there is a practical lower bound to the minimum dimension available to the designer. Specifically, certain transient events, for example, hard landings, high g-rate turns, thermal conditions, or even high turbulence can cause the shafts of the engine to flex, dramatically decreasing the tip clearance. If the design tip clearance were too small, these transient events could cause the rotor to physically strike a portion of the casing. If this occurs, both the casing and the rotor will be damaged and the clearance between the rotor tip and casing will be permanently increased. This increased clearance will result in a permanent decrease in aerodynamic performance of the gas turbine engine until the damaged components can be removed and repaired or replaced.
As can be seen, a design trade-off exists between maximizing engine performance through the minimization of component clearances versus increasing the clearances to accommodate expected transient conditions. For example, if the tip clearance is made larger, the performance of a new engine will not be as good, but the engine will be less likely to suffer a permanent decrease in performance caused by a casing rub event. It should be appreciated that this design trade-off owes its existence in no small part to the conventional gas turbine engine designs in common use today. Specifically, the inner surface of conventional casings is made of solid material, either a single metal or some type of composite. While this material is adequate for maintaining design clearances, it is also very unforgiving and inevitably sustains permanent damage when casing rub events occur.
A need exists therefore for a gas turbine engine having minimum clearances for optimizing performance, yet is capable of sustaining expected transient operating conditions including casing rub events without suffering damage.
It is therefore a primary object of the present invention to provide a gas turbine engine having a compliant casing to enable use of minimum component clearances yet accommodate casing rub events, sustaining no permanent engine damage.
It is another object of the invention to provide a gas turbine engine having a rub tolerant compliant casing including brush seals to accommodate transient rub events.
It is still another object of the present invention to provide a gas turbine engine having a compliant casing including a plurality of sets of brush seals placed in the areas between the compressor rotor tips and the stationary compressor casing.
It is still another object of the present invention to provide a gas turbine engine having a compliant casing including a plurality of sets of brush seals placed in the areas between the compressor stator tips and the rotating compressor hub.
Additional objects, advantages and other novel features of the invention will be set forth, in part, in the description that follows and will, in part, become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects and in accordance with the purposes of the present invention as described herein, a gas turbine engine having a compliant casing is described. The compliant casing enables the utilization of minimum clearances for optimizing engine efficiency while providing a deformable, resilient surface for accommodating casing rub events, sustaining no physical damage.
The preferred embodiment of the turbine engine having a compliant casing selected to illustrate the teachings of the present invention includes a number of brush seals received within the spaces between the rotor blade tips and the stationary casing and between the stationary blade tips and the rotating hub. The best mode of practicing the invention also contemplates the placement of brush seals between the rotor blade tips and the stationary casing, or, alternatively, between the stationary blade tips and the rotating hub. The brush seals provide the twofold advantages of enabling the turbine engine to utilize minimum clearances between components while being deformable to sustain rub events.
Conventional gas turbine engine technology teaches the use of solid inner casing surfaces. These solid surfaces are made of either a single metal or some type of composite. While this choice of material is adequate for maintaining design clearances, these surfaces are very unforgiving and inevitably sustain permanent damage when casing rub events occur. This has the undesirable result of permanently reducing engine efficiency until the engine can be removed and the damaged parts replaced.
Advantageously, the annular brush seals are incorporated within either or both the rotor and stator passages in order to optimize engine efficiency. The provision of brush seals in the areas between rotating and stationary components in the compressor section provides for a deformable surface capable of tolerating rub events while serving to minimize machine clearances, enhancing engine efficiency throughout the range of expected operating conditions.
Advantageously, therefore, the undesirable effects of casing rub events can be avoided by the teachings of the present invention as well as optimizing turbine engine efficiency.